Having a characteristic that is better than that of silicon as a semiconductor material that has been most frequently used in recent years, a compound semiconductor material such as silicon carbide, gallium nitride (GaN) and aluminum nitride has been extensively studied as the next generation semiconductor material. Particularly, silicon carbide has excellent mechanical strength, thermal stability, and chemical stability, very high thermal conductivity of 4 W/cm2 or more, and an operation critical temperature of 650° C. or less, which is even higher than the operation critical temperature of 200° C. or less of silicon. Further, when a crystalline structure is 3C silicon carbide, 4H silicon carbide, and 6H silicon carbide, band gaps are 2.5 eV or more, which is two times higher than that of silicon, such that silicon carbide is very useful as a semi-conductor material for high electric power and low loss conversion devices and, recently, has been considered as a light semiconductor such as an LED and a semi-conductor material for converting electric power.
Typically, examples of a process for growing a silicon carbide single crystal include an Acheson process for reacting carbon and silica in a high temperature electric furnace at 2000° C. or more, a sublimation process for sublimating silicon carbide as a raw material at a high temperature of 2000° C. or more to grow the single crystal, and a chemical vapor deposition process for performing chemical deposition using a gas source.
In the processes, it is very difficult to manufacture a silicon carbide single crystal having high purity using the Acheson process, and the silicon carbide single crystal is grown in a limited thickness to form a thin film by the chemical vapor deposition process. Accordingly, studies of growth of the silicon carbide single crystal are focused on the sublimation process for sublimating silicon carbide at high temperatures to grow crystals.
However, the sublimation process is typically performed at a high temperature of 2200° C. or more and has a strong possibility of generating various faults such as a micropipe and stacking faults, thus being limited in terms of costs of production.
A liquid phase growth process using a Czochralski process is used to grow a silicon carbide single crystal, avoiding disadvantages of the sublimation process. The liquid phase growth process for silicon carbide single crystal typically includes charging silicon or silicon carbide powder in a graphite crucible, increasing the temperature to about 1600 to 1900° C., and coming the silicon carbide seed disposed at an upper side of the crucible into contact with molten liquid to grow crystals from the surface of the silicon carbide seed. However, the process has low economic efficiency because of a very low crystal growth speed of 50 μm/hr or less.